1. Field of the Invention
The present invention relates to control of a fuel injection valve performing a fuel injection to an internal combustion engine for vehicle and, more specifically, to a control device of a fuel injection valve for driving the fuel injection valve at a high speed.
2. Description of the Related Art
A vehicle is generally mounted with: a sensor for detecting various information in accordance with operating conditions of an internal combustion engine; and control means that operates a valve-opening time and a valve-opening time period of a fuel injection valve on the basis of information from the sensor, and determines an amount of fuel to be supplied to the internal combustion engine to drive the fuel injection valve. This control means includes: valve-opening signal generation means for operating the above-mentioned valve-opening time and valve-opening time period to output an valve-opening signal; power feed control means for driving rapidly at a high voltage an electromagnetic valve of the fuel injection valve in response to the foregoing valve-opening signal and thereafter holding an open valve at a low current; and a power supply apparatus for supplying an electric power to the valve-opening signal generation means and power, feed control means and generating a drive electric power for the fuel injection valve. Hitherto, several attempts have been proposed in the field of arts as follows.
According to the art disclosed in the Japanese Patent Publication (unexamined) No. 71639/1995 (pages 2-4, FIG. 1), a battery power supply, a conduction control transistor and an electromagnetic valve are connected in series. Further provided is an auxiliary power supply for supplying a large current to the electromagnetic valve at the time of closing a circuit of the conduction control transistor. This auxiliary power supply consists of a voltage step-up DCxe2x80x94DC converter and a capacitor for charging a step-up DC voltage. During a predetermined time period at early times of conducting an electric power to the electromagnetic valve, the conduction control transistor is brought into a full conduction state to conduct a current from the auxiliary power supply as well as a current from a battery power supply. Thereafter, the conduction control transistor is subject to conduction control for constant current control. In this arrangement, a predetermined time period at early times of conduction is set to be a sum of a time period when a needle of the electromagnetic valve is full-lifted and a time period when no bound of the needle is observed.
According to the art disclosed in the Japanese Patent Publication (unexamined) No. 234793/2001 (pages 4-6, FIGS. 1 and 2), an electromagnetic valve is provided with: a power feed circuit from a capacitor that charges a step-up DC voltage by means of a voltage step-up DCxe2x80x94DC converter; a power feed circuit from a battery power supply including a back-flow prevention diode; and a current control element for ON/OFF controlling a current flowing through the electromagnetic valve. To this current control element, a current detection resistor is connected in series. First, a step-up voltage is applied to the electromagnetic valve in response to a valve-opening signal, and the electromagnetic valve is driven at a large current. When this current is lowered to a predetermined value, the power feed is switched to be fed from the battery power supply, and a constant current is conducted in response to outputs from the current detection resistor. An electromagnetic energy of the electromagnetic valve when the current control element is OFF is refluxed to the capacitor by means of the diode.
According to the art disclosed in the Japanese Patent Publication (unexamined) No. 351039/1999 (pages 4-6, FIGS. 1 through 3), an electromagnetic valve is driven at a large current at early times of driving, and thereafter driven at a constant current for a predetermined time period. In this known art, a constant voltage circuit outputting a constantly high voltage and a large capacity of capacitor to be charged by this constant voltage circuit are employed as a power supply for driving the electromagnetic valve at a large current level. Further, by automatically performing charge of the capacitor without regard to whether the electromagnetic valve is ON/OFF, opening the valve driven at a large current level can be conducted up to a region of high-speed rotation.
According to the art disclosed in the Japanese Patent Publication (unexamined) No. 269404/1995 (pages 4-6, FIG. 1), an electromagnetic valve is driven by: peak current supply means for conducting a peak current for opening the valve at a high speed upon start-up of the conduction; and holding current supply means for conducting a holding current smaller than the peak current after the peak current has been conducted. In this known art, fault is determined from a charging voltage of a capacitor that charges a step-up voltage, when a step-up circuit for conducting the peak current is faulty. Upon determination of a fault, a valve-opening time is made earlier, and a valve-opening time period is increased, thereby leading to prevention of engine stall.
Among the conventional arts as described above, the art disclosed in the Japanese Patent Publication (unexamined) No. 71639/1995 (pages 2-4, FIG. 1) intends to assist a valve-opening drive energy and reduce load on a high-voltage auxiliary power supply by not solely depending on a step up voltage having been charged at a capacitor in order to get a drive energy for a predetermined time period at early times of conduction to an electromagnetic valve, but also bringing the conduction control transistor into a state of a full conduction to feed the whole voltage from a battery. However, there is no switching means between the capacitor and the electromagnetic valve, and therefore charging to the capacitor cannot be performed during valve open holding time period. Thus, a problem exists in that any follow-up to a region of rotation at a high speed is hard to do, as well as valve-opening drive energy significantly varies due to voltage of the battery resulting in instability of fuel injection characteristic.
In the art disclosed in the Japanese Patent Publication (unexamined) No. 234793/2001 (pages 4-6, FIGS. 1 and 2), since the switching element supplying a high voltage from a capacitor and the switching element applying voltage from a battery are provided, it is certain that sharing of a drive energy at the time of opening the valve is performed with accuracy. An object of this known art, however, is to return to a capacitor an electromagnetic energy having been charged at the electromagnetic valve. Thus a problem exits in that accuracy in controlling a holding current by means of a current control element decreases. That is, a feed current to the electromagnetic valve flows to a current detection resistor as it is when the current control element is in conduction. On the other hand, an induction current of the electromagnetic valve flows dividedly to the capacitor and the current detection resistor when the current control element is in a state of open circuit. Therefore, detection current at the current detection resistor is not coincident with a current flowing through the electromagnetic valve. Further, ripple of the current flowing through the electromagnetic valve becomes larger when the current control element is ON/OFF, and it is necessary that a holding current is kept at a sufficient level in order to hold an open valve without fail. As a result, heat generation at the electromagnetic valve or current control element is increased, and energy loss is increased.
In the art disclosed in the Japanese Patent Publication (unexamined) No. 351039/1999 (pages 4-6, FIGS. 1 through 3). In the same manner as in the Japanese Patent Publication (unexamined) No. 234793/2001, switching elements are separately provided so that sharing a drive energy at the time of opening the valve is performed with accuracy. The current flowing through the electromagnetic valve returns to a communicating diode at the time of constant current control in order to hold valve open. Further provided is a switching element for interrupting an excitation current to, the electromagnetic valve at a high speed. However, in the case of occurrence of any short-circuit error that is incapable of opening a circuit of a transistor for applying a high voltage to the electromagnetic valve, the switching element is brought into an open circuit under the application state of the high voltage. Hence, a problem exists in that the switching element is liable to be damaged due to high withstanding voltage and, as a result, a solenoid of the electromagnetic valve is in danger of being burnt out.
In the art disclosed in the Japanese Patent Publication (unexamined) No. 269404/1995 (at pages 4-6, in FIG. 1), valve-opening drive is performed with a holding current by advancing the valve-opening time while extending the valve-opening time period even if it is impossible to supply the peak current. Accordingly, a problem exists in that the holding current needs to be set at an extremely great current value as compared with current required for merely holding the valve open, resulting in a larger heat generation at the electromagnetic valve. Moreover, suppression of this heat generation makes it impossible to apply a sufficiently high voltage under normal conditions to open the valve at a high speed.
The present invention was made to solve the above-discussed problems, and has an object of accomplishing a stable fuel injection in spite of voltage variation in a battery to act as a main power supply and preventing burnout and fire due to abnormal heating in spite of occurrence of short circuit fault in current control element. Another object of the invention is to obtain a control device for controlling a fuel injection valve capable of performing a reliable evacuating operation even if a high voltage auxiliary power supply for performing the rapid power feed comes to be in fault.
To accomplish the foregoing objects, a control device for controlling a fuel injection valve according to the invention includes:
an auxiliary power supply for stepping up voltage from a main power supply mounted on a vehicle;
a first switching element for conducting voltage from the auxiliary power supply to an electromagnetic solenoid for driving a fuel injection valve;
a second switching element for conducting voltage from the main power supply to the electromagnetic solenoid;
a third switching element that possesses a withstanding voltage limiting characteristic larger than a maximum output voltage from the auxiliary power supply, and interrupts a supply current to the electromagnetic solenoid at a high speed;
current detection means for detecting conduction current to the electromagnetic solenoid;
valve-opening signal generation means for inputting an operation information of an internal combustion engine and outputting a valve-opening signal and a valve-opening drive signal corresponding to a valve-opening time and a valve-opening time period of the fuel injection valve; and
conduction control means for controlling a power feed to the electromagnetic solenoid in response to a signal of the valve-opening signal generation means.
In the mentioned control device for controlling a fuel injection valve, the conduction control means performs a rapid power feed from the auxiliary power supply to the electromagnetic solenoid by means of the first switching element in response to the valve-opening drive signal from the valve-opening signal generation means. Subsequently, the conduction control means performs a continuous power feed from the main power supply by means of the second switching element. Further, the conduction control means performs a hold power feed under ON/OFF control of the second switching element by feedback control based on a current value detected by the current detection means during continuance of the valve-opening signal after the valve-opening drive signal has ended. Furthermore, the conduction control means interrupts a power feed to the electromagnetic solenoid at a high seed by means of the third switching element immediately after, the valve-opening signal has ended. In the mentioned conduction control, minimum value of an output voltage from the auxiliary power supply is set to be larger than a maximum value of voltage of the main power supply, and a step-up operation of the auxiliary power supply is stopped during the rapid power feed.
As a result of above arrangement, energy for the rapid power feed at the time of opening the valve does not come under the influence of a voltage variation in on-vehicle battery acting as the main power supply. Thus, a valve-opening operation can be performed stably, and the auxiliary power supply can be prevented from over-load. Furthermore, the step-up of voltage is started immediately after the rapid power feed to be capable of obtaining a stable high voltage, thereby enabling to achieve a smaller-sized auxiliary power supply at a reasonable cost. Besides, it is possible to set the power feed reliably in three stages of rapid power feed, continuous power feed and holding power feed, as well as the switching elements can be shared or commonly used in performing control of the continuous power feed and holding power feed. Consequently, it can be achieved easily to limit a current value of the holding power fed to the minimum holding current to suppress temperature rise in the electromagnetic solenoid, and reduce number of parts as well.